This invention relates to a colorless, transparent and nearly nonexpansive glass-ceramic which uses a SiO.sub.2 -Al.sub.2 O.sub.3 -Li.sub.2 O base glass with addition of ZrO.sub.2 as a nucleating agent and contains fine crystals of .beta.-quartz and .beta.-eucryptite.
There are various uses for transparent glass-ceramics, and accordingly there are various proposals of glass-ceramics high in transparency.
JP No. 36-15172 shows producing a transparent glass-ceramic by using a SiO.sub.2 -Al.sub.2 O.sub.3 -Li.sub.2 O base glass with addition of TiO.sub.2 as a nucleating agent, and there are other proposals of using TiO.sub.2 or a combination of TiO.sub.2 and ZrO.sub.2 as a nucleating component for prducing transparent glass-ceramics. However, the inclusion of TiO.sub.2 results in yellowish or brownish coloring of the obtained glass-ceramics. Transparent but colored glass-ceramics are not suitable for use in heat-resistant monitoring windows, aircraft windshields, electronic device substrates, etc.
JP No. 42-21357 proposes to produce a transparent and colorless or slightly whitish glass-ceramic by adding 2-15 wt % of ZrO.sub.2 to a glass composition composed of SiO.sub.2, Al.sub.2 O.sub.3 and at least one of MgO, Li.sub.2 O and ZnO. However, glass-ceramics according to this proposal generally exhibit considerable thermal expansion and are not always very high in transparency.
JP-A No. 64-52631 proposes to use a combination of ZrO.sub.2 and SnO.sub.2 as a nucleating component for producing a glass-ceramic using a SiO.sub.2 -Al.sub.2 O.sub.3 -Li.sub.2 O base glass. However, the addition of SnO.sub.2 is liable to cause precipitation of coarse crystals which render the glass-ceramic cloudy or opaline. Besides, when SnO.sub.2 is used the heat treatment of the glass for crystallization requires a very strict and intricate control technique.